1. Field of the Invention
The present invention relates to a light emitting apparatus that enables light emitting, such as white light, using a semiconductor light emitting diode (LED) element and a phosphor that changes a wavelength of output light from the light emitting diode (LED) element; a lighting device using the light emitting apparatus as a light source; and a liquid crystal display apparatus using the light emitting apparatus as a backlight.
2. Description of the Related Art
A conventional light emitting apparatus, such as a lighting device, using a semiconductor light emitting diode (LED) element has been used for various purposes. A light emitting apparatus capable of having more color rendering properties and emitting more natural white light is in need. In particular, the emission of white light adjusted to the path of black body radiation is known to provide people a visual sense of security and have a calming effect to provide people a sense of serenity.
For example, Reference 1 discloses an LED lighting apparatus that includes a light emitting portion having a red LED, a blue LED and a green LED, and a light receiving sensor for measuring light outputted from the light emitting portion. The LED lighting apparatus obtains white light by adjusting driving current value provided to respective LEDs so that the LED lighting apparatus obtains a predetermined white balance, such as white color on the path of black body radiation (black body radiation locus), based on a measured value from the light receiving sensor.
FIG. 8 is a table showing emission spectra of a blue LED, a green LED and a red LED.
As can be seen from FIG. 8, the emission of each of the three primary color LEDs of blue, green and red is narrow in the half width and high in color purity. Therefore, there is a significantly dark wavelength region in white light by the emission of the three primary color LEDs because there are valleys between the emission spectra of the blue LED and the green LED, and between the emission spectra of the green LED and the red LED.
FIG. 9 is a diagram showing the chromaticity coordinates of each of the three primary color LEDs so as to obtain white light.
As shown in FIG. 9, the chromaticity coordinates (x, y) of the blue LED are (0.152, 0.025), for example; and the chromaticity coordinates (x, y) of the green LED are (0.194, 0.725), for example; and the chromaticity coordinates (x, y) of the red LED are (0.696, 0.304), for example, in order to obtain white light.
FIG. 10 is a CIE 1931 chromaticity diagram showing the chromaticity coordinates of the respective color LEDs in FIG. 9 to obtain white light, the chromaticity diagram explaining the relationship between the emission of the blue, green and red LEDs and the black body radiation locus.
In FIG. 10, the emission of the three primary color LEDs is plotted in the CIE 1931 chromaticity diagram using the chromaticity coordinates shown in FIG. 9, and emission intensity for respective colors is adjusted to generate colors inside the triangle formed by the respective three color LEDs. In addition, as can be seen in FIG. 10, the emission of the respective LEDs also extends to the perimeter of the CIE 1931 chromaticity diagram, thereby generating a wide range of colors. Making the most of this characteristic, LEDs are employed for a variety of display devices, such as a backlight for a liquid crystal display apparatus.
Further, Reference 2 discloses a white light LED that includes a blue LED and two types of phosphors as encapsulating resins for the blue LED. The wavelength of the emitted light from the blue LED is converted by the phosphors, so that this white light LED obtains a white light with a color temperature of 2300 K to 7000 k.
Reference 1: Japanese Laid-Open Publication No. 2004-253309
Reference 2: Japanese Laid-Open Publication No. 2007-507096